Recent studies postulate that newborn hamsters with maternal measles antibody survive a lethal dose of HNT virus and, in time, some of the animals are affected with a latent CNS infection that resembles SSPE. It has been hypothesized that the presence of measles antibody associated with an immature cellular immunity is crucial for the production of the SSPE-like syndrome. This project proposes to investigate the theorized role of antibody and delayed hypersensitivity in the development of chronic brain infection following HNT inoculation. This study will conduct careful follow-up of all animals to distinguish between survivors with no evidence of virus and survivors undergoing suppressed measles brain infection. This distinction will be done through immunofluorescence, histopathology, tissue culture possible involvement of antibody and/or delayed hypersensitivity in the immunopathogenesis of the SSPE-like hamster disease.